1. Technical Field
This disclosure relates to amplifiers and, more particularly, to providing common mode input control for a capacitively-coupled amplifiers in a pipeline analog-to-digital converter (ADC).
2. Description of Related Art
Pipeline ADCs implemented on fine line CMOS processes may require amplifiers having large signal swings, as compared to the power supply, to maximize signal-to-noise ratio. These amplifiers may be differential and require a circuit to control the output common mode level, commonly referred to as common mode feedback (CMFB) circuit. In addition to output common mode control, the input common mode voltage may also be controlled.
Some of these circuits may use an Input Common Mode (ICM) bias generator to provide this control. However, the output impedance of the Input Common Mode bias generator may need to be very low to ensure fast common mode settling for the preceding stage amplifier. This may require a significant amount of additional power or an additional package pin with external bypass. Either approach may be costly.
There thus is a need to control the input common mode voltage in a way that is not as costly.